Lateral-flow type devices for the detection and quantification of an analyte of interest in a fluid sample are well known. Generally, the devices include a solid phase fluid permeable flow paths through which fluid travels by capillary force. The flow paths have immobilized thereon various binding reagents for the analyte (or analog thereof), other binding partners, or conjugates involving binding partners for the analyte and members of signal producing systems (e.g., a label). The various assay formats (e.g. competitive, sandwich, and blocking) used with these devices are well known for the direct or indirect detection of the analyte of interest in the test sample.
In using lateral flow devices to conduct an assay, sample preparation is important to the function of the assay. Importantly, the devices rely on sufficient sample volume so that the matrix can be sufficiently wetted to allow for lateral flow of the sample liquid. Thus, samples often need to be diluted when sample volumes are small. For blood samples, large volumes can be centrifuged to remove red blood cells and other blood components. But for small volumes, such as the volume from a finger prick, centrifuging is not practical. In some cases, the devices include a filter to remove some of the sample's solid or cellular components. In such cases, the filters themselves absorb a significant sample volume.
Sample volume is one way of controlling the sensitivity of the assay, since enough sample is necessary in order to provide a detectable quantity of the analyte. For small volume sample, one way to control sensitivity of the assay is to control how the sample is added to the device. Numerous ways are known for adding sample to solid phase flow paths of lateral flow devices. For instance, sample may be added directly to the flow path or to a sample holder. Such devices are described in U.S. Pat. Nos. 4,943,522, 4,956,302; 5,939,331; 6,468,474; 6,607,922; 6,686,208; and 6,706,539, each of which is incorporated by reference herein in its entirety. In addition to sensitivity, the ease of operator use and the minimization of steps are commercially desirable features. Thus, ways to decrease sample and reagent handling, while maintaining assay sensitivity, are important aspects of developing lateral flow devices.